With folders I have noticed that it is the uncirculated or nearly uncirculated coins that have the problem of not fitting.
My guess is that Whitman, and other folder manufacturers, deliberately 'size' the holes to fit the more worn circulated coins.
I believe that if they sized the holes for the larger, less circulated coins, then the smaller, more worn coins would often fall out of the holders.
This way (sized for the smaller coins) everything stays in, although not without a lot of careful effort getting the newer coins in.